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Message: <blockquote data-quote="AuroraGirl" data-source="post: 28298" data-attributes="member: 9417">i use 12.9 often since i source from menards a lot, and flanged head bolts or ones in the large size (m12, m14 etc) there tend to be in black phosphate coating vs cheap plating, and thats preferabnle to the cheap plating and non flange head ones. 12.9 hardness means cutting or drilling is a CHORE so buy one close to the length you need or use a bolt cutter to rough the size and have threaded nuts on it to back off to fix the thread and touch it up with a thread file12.9 means its not as flexible of course because of the hardness ,but ive had no issues on my suspension/brakes/trailer hitch etc but I for sure would be mindful of things when gm says 9.8 vs 10.9 , because there may be a reason they wanted 9.8 or it may be just they only needed it that much but more wouldnt hurt.  8.8 would be like grade 5 for reference 9.8 , 10.9 are closest to grade 8, 10.9 has no equivalent that I know of</blockquote>